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Old 7th September 2009, 02:04 PM
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Default Filter factors

Hi,
I've read a couple of times that some photographers are taking a reading through the filter before applying the filter factor. If you do that for example with a yellow filter with a factor of 2. What exposure factor are you giving to film after that? What about a green filter (2 stops), red filter (3 stops)....
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Old 7th September 2009, 03:25 PM
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The theory is that you do not then apply any filter factor as you have taken the reading with the filter in place. However, many will argue that as a meter's colour response is not the same as the film's, this is at best only an approximation and for deep filters, such as a deep red or polariser, is likely to be so far out as to be pointless. Some meters claim to be modified to reflect film sensitivity (the Zone IV modified Pentax spotmeter comes to mind) but there have been doubts expressed about the reality of that too.

I do not meter through the filter but apply the filter factor - usually the one suggested by the manufacturer. I often bracket in any case so any inaccuracy in the filter factor is generally taken care of.
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Old 7th September 2009, 03:44 PM
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I agree with Bob; it is far better applying the filter factor manually rather than letting the camera meter do this. (Meter – fit filter – apply filter factor).
In fact for some of my filters I have a printed 'aide-mémoire' on the case, after doing some testing for the film and developer – using a Kodak colour test card.

David.
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Old 7th September 2009, 05:21 PM
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Thank you guys. I will continue to apply the filter factor.
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Old 8th September 2009, 07:17 AM
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I don't meter through the filter but I set to meter's ISO to the films equivalent speed with the filter fitted.

e.g. If I have ISO 400 film and a red filter which needs a 3 stop compensation, I set the meter ISO to 50.


Steve.
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Old 8th September 2009, 08:26 AM
Dave miller Dave miller is offline
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Quote:
Originally Posted by Steve Smith View Post
I don't meter through the filter but I set to meter's ISO to the films equivalent speed with the filter fitted.

e.g. If I have ISO 400 film and a red filter which needs a 3 stop compensation, I set the meter ISO to 50.


Steve.
Which is what I do, and then usually forget to change it with the filter.
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Old 8th September 2009, 12:52 PM
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I tend to do it on the camera: take a reading and set the speed & f-stop on the camera and then either open the aperture or use a slower speed depending on which is more important (except for the times I close the aperture or increase the speed during a photo-dyslexia event ).
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Old 8th September 2009, 08:02 PM
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Quote:
Originally Posted by Steve Smith View Post
I don't meter through the filter but I set to meter's ISO to the films equivalent speed with the filter fitted.

e.g. If I have ISO 400 film and a red filter which needs a 3 stop compensation, I set the meter ISO to 50.


Steve.
I understand what you do. But let's say that your development times are set to 400 ISO but you change it to 50 ISO, then your development times are not good anymore. Isn’t true?
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Old 8th September 2009, 08:12 PM
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Use the same development time for 400 iso, you are setting your meter to the lower setting simply to take into account the filter factor, but the film is still 400,this is the way I do it and I have done so for many years,but DO NOT change the dev times, dev as for 400,Richard
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Old 8th September 2009, 08:14 PM
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I think it is not true. You are giving the film the correct amount of light appropriate for the box speed. The light has been dimmed by the filter so you need to open up the aperture or slow the shutter speed in the same way as someone dimming the lights. I guess altering the ASA rating is one way to offset the the reduced light levels and get a correct exposure reading.
Tony
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